The rapid development of wireless communication technologies enables a new challenge to the application fields looked possible in virtual reality, and hence many of the application fields have been implemented and realized immediately accordingly.
Among others, most notable fields are U-City using USN (Ubiquitous Sensor Network), Femtocells that enable home networks, Robots that play the role of home helpers, unmanned aircraft that carry out emergency missions during the war operations, space solar generation that can be solved the energy of the future and the environmental issues, etc. In such application fields, information collected in each field is used to permit recognition, prevention and control of various matters.
However, the systems applied to these application fields have a capability of performing wireless communications, but they have still manifested the problem in terms of the energy supply and transfer. So, it cannot be said that the systems are a wireless system or a wireless communication system in the true sense. In addition, these systems have an extremely dominant problem in the life of the battery and fuel, an amount of energy that can be transferred in a wireless manner.
In addition, the electric toothbrushes, notebooks, Walkman, and the like have been adopted an inductance coupling technique by electromagnetic waves so-called an electromagnetic induction method. However, the inductance coupling technique by electromagnetic waves has a drawback that energy transfer efficiency deteriorates rapidly if the coupling coefficient of inductors is not high and hence wireless energy transfer is not possible when leaving a specific location.
Thus, in order to solve the problems such as low power, transfer distance, an amount of energy that can be transferred, lasting operational time, and the like, there has been developing magnetic resonance techniques that are similar to the electromagnetic induction method but are designed to concentrate the energy at a specific resonance frequency through the use of inductors and capacitors to transfer power in the form of magnetic energy.
In a wireless energy transfer structure using such magnetic resonance techniques has a merit that it can transfer the energy with relatively high power to several meters compared to the electromagnetic induction method. Nevertheless, it requires a high resonance characteristic, i.e., high quality factor.
On the other hand, meta-materials collectively refer to substances that are artificially synthesized to exhibit distinct electromagnetic properties that are not common in nature.
The radio waves in most materials are propagated in compliance with the right-hand rule of the vector fields E, H, and β, where E is an electric field, H is a magnetic field and β is a wave vector. The direction of the phase velocity is the same as the direction of energy signal propagation (group velocity), and the refractive index is a positive number. The material having the above properties refers to as a Right Handed (RH) material. Most natural materials are RH materials. Artifacts are also the RH materials.
The meta-material has an artificial structure. When the meta-material is designed a structural average unit cell size ‘p’ much smaller than the wavelength of electromagnetic energy that is guided by the meta-material, the meta-material can behavior like as a homogeneous medium with respect to the electromagnetic energy being guided. Unlike the RH material, the meta-material may represent a negative refractive index in which the relative direction of the vector fields (E, H, β) becomes opposite to the direction of the energy propagation and phase velocity of signals that comply with the left-hand rule. The meta-material that supports only the negative refractive index is a Left Handed (LH) meta-material.
Many of the meta-materials are a mixture of the LH meta-materials and RH meta-materials and therefore, are a Composite Right and Left Handed (CRLH) meta-materials. A CRLH meta-material may exhibit a property of an RH meta-material at a high frequency and a property of an LH meta-material at the low-frequency. The design and attribute for the CRLH meta-materials are disclosed by Christophe Caloz and Tatsuo Itoh, “Electromagnetic Metamaterial: Transmission Line Theory and microwave applications” John Wiley & Sons, 2006. The CRLH meta-materials and their applications in antennas are disclosed by Tatsuo Itoh, “invited paper: Prospects for Metamaterials”, E-Journal, Volume 40, No. 16, August 2004. Both of which are hereby incorporated by reference as if fully set forth herein.
The CRLH meta-materials may be organized and processed to represent the electromagnetic attributes, which are produced for special purposes, to use in applications where it is difficult or impractical or impossible to use other materials. Further, the CRLH meta-materials may also be used to develop new applications and organize new elements that are not possible with the RH meta-materials.
The applicant focused on the fact that the appliance of the wireless power transfer technology to meta-materials may lead to an improvement of the wireless power transfer efficiency. Of course, there exist some technologies in which the wireless power transfer technology is adopted to meta-materials, but it is hard for these technologies to enhance sufficiently the fields of electric and magnetic fields by raising the resonance characteristics of the wireless power resonator.